A conventional wireless transmitter having a function for controlling its transmitting electric power in a constant state is shown in FIGS. 1 and 2 with which an explanation therefor will be made.
FIG. 1 is a block diagram showing a constitution of a conventional first wireless transmitter wherein the wireless transmitter 200 has a function for controlling its transmitting electric power in a constant state by means of automatic level control (ALC) and which comprises a baseband transmission signal generating section 101, a baseband filter 102, a D/A converter 103, a quadrature modulator 104, a first local oscillator 105, a first variable gain amplifier 106, a first bandpass wave filter 107, a frequency converter 108, a second local oscillator 109, a second bandpass wave filter 110, a second variable gain amplifier 111, a third bandpass wave filter 112, a transmission amplifier 113, an isolator 114, a high-frequency coupler 115, an antenna sharer 116, an antenna 117, a high-frequency detector 118, an A/D converter 119, a variable gain amplifier control signal generator 120, and a target gain control signal generating section 121.
The wireless transmitter 200 provided with components 101 through 121 is classified broadly into a wireless transmitting means composed of the components 101 through 117 and a transmitting electric power control means composed of the components 118 through 121.
In the wireless transmitting means, the baseband transmission signal generating section 101, the baseband filter 102, and the D/A converter 103 are connected by baseband signal lines involving I-channel and Q-channel components (hereinafter simply referred to as “I- and Q-components”) with each other. Input ends of the quadrature modulator 104 are connected to baseband signal output ends involving I- and Q-components of the D/A converter 103 and an output end of the first local oscillator 105. An intermediate frequency output end of the quadrature modulator 104 is connected to an intermediate frequency input end of the frequency converter 108 through the first variable gain amplifier 106 and the first bandpass wave filter 107.
A radio frequency input end of the frequency converter 108 is connected to an output end of the second local oscillator 109, while a radio frequency output end of the frequency converter 108 is connected to an input end of the antenna 117 through the second bandpass wave filter 110, the second variable gain amplifier 111, the third bandpass wave filter 112, the transmission amplifier 113, the isolator 114, the high-frequency coupler 115, and the antenna sharer 116.
Furthermore, in the wireless transmitting means, an input end of the high-frequency detector 118 is connected with an output end for high-frequency detection of the high-frequency coupler 115, while an output end of the high-frequency detector 118 is connected with a transmitting electric power signal input end of the variable gain amplifier control signal generator 120 through the A/D converter 119.
A target gain signal input end of the variable gain amplifier control signal generator 120 is connected with an output end of the target gain control signal generating section 121, an intermediate frequency gain control signal output end of the variable gain amplifier control signal generator 120 is connected with a gain amplifying conversion signal input end of the first variable gain amplifier 106, and a radio frequency gain control signal output end thereof is connected with a gain amplifying conversion signal input end of the second variable gain amplifier 111.
In the following, functions of the respective components 101 through 121 are described.
The baseband transmission signal generating section 101 generates a transmission signal transmitted from the present wireless transmitter 200. The baseband filter 102 applies bandwidth limiting to a transmission signal (digital signal) from the baseband transmission signal generating section 101. The D/A converter 103 converts digital signals passed through the baseband filter 102 into analog signals.
The quadrature modulator 104 functions to frequency-convert transmission signals of baseband bandwidth from the D/A converter 103 into transmission signals of intermediate frequency bandwidth, and further to quadrature-modulate the transmission signals thus frequency-converted.
The first local oscillator 105 outputs local oscillation signal used in the quadrature modulator 104. The first variable gain amplifier 106 controls gains in response to intermediate frequency gain control signals from the variable gain amplifier control signal generator 120, thereby to amplify transmission signals from the quadrature modulator 104.
The first bandpass wave filter 107 passes through only those of intermediate frequency bandwidth among transmission signals from the first variable gain amplifier 106.
The frequency converter 108 frequency-converts the transmission signals in intermediate frequency bandwidth passed through the first bandpass wave filter 107 into those of radio frequency bandwidth.
The second local oscillator 109 outputs local oscillation signal used in the frequency converter 108. The second bandpass wave filter 110 passes through only transmission signals in radio transmission bandwidth.
The second variable gain amplifier 111 controls gains in response to radio frequency gain control signals from the variable gain amplifier control signal generator 120 to amplify transmission signals in radio transmission bandwidth passed through the second bandpass wave filter 110. The third bandpass wave filter 112 passes through only the transmission signals of radio transmission bandwidth from the second variable gain amplifier 111. The transmission amplifier 113 amplifies the transmission signals of radio transmission bandwidth passed through the second variable gain amplifier 111 to a predetermined transmitting electric power.
The isolator 114 passes through transmission signals in only a direction from the transmission amplifier 113 to the high-frequency coupler 115, while it prevents to pass through the signals in the reverse direction. The high-frequency coupler 115 takes out transmission signals in a front end of the wireless transmitter 200.
The high-frequency detector 118 detects an output electric power of the transmission signals from the high-frequency coupler 115. The A/D converter 119 converts an analog value of the electric power of the transmission signals detected in the high-frequency detector 118 into a digital value (a value of output electric power) thereof.
The variable gain amplifier control signal generator 120 is a component wherein gains of the first and second variable gain amplifiers 106 and 111 are set so as to be target gains in response to target gain control signals from the target gain control signal generating section 121 at the time of starting transmission, and signals for controlling gains of the first and second variable gain amplifiers 106 and 111 are generated in such that a value of output electric power from the A/D converter 119 comes to be constant at the time of subsequent transmission. The target gain control signal generating section 121 generates target gain control signals for setting target gains.
In the following, operations of the wireless transmitter 200 having such constitution as described above are described.
At the time of starting transmission, gains of the first and second variable gain amplifiers 106 and 111 are set so as to be target gains in response to target gain control signals from the target gain control signal generating section 121 in the variable gain amplifier control signal generator 120.
Then, baseband transmission signals of I- and Q-components generated in the baseband transmission signal generating section 101 are input to the quadrature modulator 104 through the baseband filter 102 and the D/A converter 103 wherein the baseband transmission signals thus input are subjected to frequency conversion into transmission signals of intermediate frequency bandwidth in response to local oscillation signals from the first local oscillator 105, and further the signals thus converted are subjected to quadrature modulation.
The transmission signals in intermediate frequency bandwidth are amplified by the first variable gain amplifier 106 target gains of which have been set at the time of starting transmission, the signals amplified are filtered by the first bandpass wave filter 107, and then, they are frequency-converted by means of the frequency converter 108 into transmission signals of radio frequency bandwidth in response to local oscillation signals from the second local oscillator 109.
The transmission signals of radio frequency bandwidth are filtered by the second bandpass wave filter 110, the signals thus filtered are amplified by the second variable gain amplifier 111 target gains of which have been set at the time of starting transmission, then, the amplified signals are filtered by the third bandpass wave filter 112, and the signals filtered are amplified by the transmission amplifier 113. The resulting amplified transmission signals are transmitted wirelessly from the antenna 117 to, for example, a base station (not shown) through the isolator 114, the high-frequency coupler 115, and the antenna sharer 116.
A transmitting electric power transmitted from the antenna 117 is detected by the high-frequency detector 118 through the high-frequency coupler 115, an analog value of an electric power of the transmission signals thus detected is converted into a digital value (a value of output electric power), and the value is input to the variable gain amplifier control signal generator 120. From the variable gain amplifier control signal generator 120, intermediate frequency gain control signals are output to the first variable gain amplifier 106 and radio frequency gain control signals are output to the second variable gain amplifier 111 in such that the output electric power value becomes constant, whereby transmitting electric power is controlled at a constant value.
FIG. 2 is a block diagram showing a constitution of a conventional second wireless transmitter wherein like or corresponding components of FIG. 1 are designated by the same reference characters in FIG. 2 and the description therefor is omitted.
A wireless transmitter 300 shown in FIG. 2 has a function to control a transmitting electric power at a constant value even in a case when temperature changes. The wireless transmitter 300 is composed of a variable gain amplifier control signal generator 122, a temperature sensor 123, and an A/D converter 124 other than the following components, which have been described with respect to FIG. 1, i.e., a baseband signal generating section 101, a baseband filter 102, a D/A converter 103, a quadrature modulator 104, a first local oscillator 105, a first variable gain amplifier 106, a first bandpass wave filter 107, a frequency converter 108, a second local oscillator 109, a second bandpass wave filter 110, a second variable gain amplifier 111, a third bandpass wave filter 112, a transmission amplifier 113, an isolator 114, an antenna sharer 116, an antenna 117, and a target gain control signal generating section 121.
The temperature sensor 123 detects ambient temperatures. The A/D converter 124 converts an analog amount of temperature detected by the temperature sensor 123 into a digital amount (a temperature value). In the variable gain amplifier control signal generator 122, gains of the first and second variable gain amplifiers 106 and 111 are set so as to become target gains in response to target gain control signals from the target gain control signal generating section 121 at the time of starting transmission.
Furthermore, the variable gain amplifier control signal generator 122 maintains a table wherein temperature values are allowed to correspond to gains in a memory, retrieves gains corresponding to temperature values from the A/D converter 119 at the time of starting transmission, and generates a signal for controlling gains of the first and second variable gain amplifiers 106 and 111 in such that they coincide with the gains retrieved.
In the following, operations of the wireless transmitter 300 having the above-described constitution are described.
At the time of starting transmission, gains of the first and second variable gain amplifiers 106 and 111 are set to target gains in the variable gain amplifier control signal generator 120 in response to a target gain control signals from the target gain control signal generating section 121.
Then, baseband transmission signals of I- and Q-components generated in the baseband transmission signal generating section 101 are input to the quadrature modulator 104 through the baseband filter 102 and the D/A converter 103 wherein the signals are frequency-converted into transmission signals of intermediate frequency bandwidth, and further they are quadrature-modulated in response to local oscillation signals from the first local oscillator 105.
The transmission signals of intermediate frequency bandwidth are amplified in the first variable gain amplifier 106 wherein target gains have been set at the time of starting transmission, the signals thus amplified are filtered by the first bandpass wave filter 107, and then, the signals filtered are frequency-converted into transmission signals in radio frequency bandwidth in response to local oscillation signals from the second local oscillator 109.
The transmission signals of radio frequency bandwidth are filtered by the second bandpass wave filter 110, the signals thus amplified are in the second variable gain amplifier 111 wherein target gains have been set at the time of starting transmission, then, the signals amplified are filtered by the third bandpass wave filter 112, and the signals thus filtered are amplified in the transmission amplifier 113. The amplified transmission signals are transmitted wirelessly from the antenna 117 to, for example, a base station through the isolator 114, and the antenna sharer 116.
In case of the transmission, an ambient temperature is detected by the temperature sensor 123, an analog amount of the temperature thus detected is converted into a digital value (temperature value) by means of the A/D converter 124, and the resulting value is input to the variable gain amplifier control signal generator 122.
In the variable gain amplifier control signal generator 122, gains corresponding to the temperature values input are retrieved from a table, and gains of the first and second variable gain amplifiers 106 and 111 are controlled in such that they come to be the gains retrieved. The control is conducted in accordance with a step wherein intermediate frequency gain control signals are output to the first variable gain amplifier 106, and a step wherein radio frequency gain control signals are output to the second variable gain amplifier 111.
According to such constitution as described above, transmitting electric power is maintained at a constant value even in a case where ambient temperature varies.
In the meantime, for the sake of suppressing electric power consumption in recent years, a conventional wireless transmitter has been adapted to apply such a technique that if there is no signal to be transmitted in spite of connection of radio link, for example, there is no conversation during phone call, no audio data is transmitted.
In this case, since no audio data is transmitted, the whole level of a transmission output decreases. However, it is desired that a level of control data is constant irrespective of ON/OFF of such audio data.
In this respect, however, a conventional ALC in the wireless transmitter 200 shown in FIG. 1 operates in such that even level changes due to ON/OFF of audio data are compensated, and a level in control data is amended also at the time of the compensation. Accordingly, there is such a problem that a level of control data cannot be maintained at a constant value.
On the other hand, there is such a constitution that the wireless transmitter 300 shown in FIG. 2 is provided with the temperature sensor 123 to compensate temperature changes for the sake of stabilizing output electric power with respect to such temperature changes.
In this case, however, it is required to prepare a table for compensation of temperature. Besides, it is also required to operate adjustments in preparation of a table for temperature compensation in each transmitter in order to control correctly data, because there are individual specificities in temperature sensors 123 and heat sources. Thus, there is a problem of troublesome man-hours for the preparation.